Heating Systems for a Refrigeration System

The present disclosure relates to heating systems for a refrigeration system (e.g., a transport refrigeration system). The present disclosure also relates to refrigeration systems comprising such heating systems.

It is increasingly desirable to use process fluids (e.g., refrigerants) with relatively low global warming potential (GWP) in refrigeration systems, including in transport refrigeration systems. However, such refrigerants have some properties which are significantly different from corresponding properties of traditional refrigerants. These different properties are associated with both performance and safety challenges in the context of refrigeration systems.

The embodiments described herein have been devised with the foregoing in mind.

According to a first aspect there is provided a heating system for a refrigeration system, the heating system comprising: a heater; power terminals configured to receive electrical power from a source; a heater temperature sensor module configured to change from a first state to a second state when a temperature associated with the heater reaches or exceeds a heater temperature action threshold; and an electrical interlock arrangement configured to prevent supply of electrical power from the power terminals to the heater when the heater temperature sensor module is in the second state.

It may be that the heater temperature sensor module comprises a bimetallic switch.

The heating system may comprise a supply switch located between the power terminals and the heater. The electrical interlock arrangement may be configured to prevent supply of electrical power from the power terminals to the heater when the heater temperature sensor module is in the second state by causing the supply switch to be in a non-conducting state.

The heating system may comprise a pathway for conveying a refrigerant. The heater temperature action threshold may be at least 100° C. lower than an autoignition temperature of the refrigerant. The heater temperature action threshold may be no greater than 200° C.

It may be that the heating system comprises a controller configured to determine whether the heater temperature sensor module is in the first state or the second state.

The heating system may comprise a semiconductor switch operable to modulate supply of electrical power from the power terminals to the heater. The heating system may further comprise a driver module configured to control the semiconductor switch based on a drive signal.

According to a second aspect there is provided a heating system for a refrigeration system, the heating system comprising: a heater disposed within a space; power terminals configured to receive electrical power from a source; a semiconductor switch operable to modulate supply of electrical power from the power terminals to the heater; a driver module configured to control the semiconductor switch based on a drive signal; an interruption switch configured to prevent the driver module from receiving the drive signal when in a non-conducting state; and a concentration sensor module configured to: monitor a concentration of refrigerant in the space; and cause the interruption switch to be in the non-conducting state when the monitored concentration of refrigerant reaches or exceeds a concentration action threshold.

The heating system may comprise a controller configured to determine whether the interruption switch is in the non-conducting state.

In accordance with the first aspect and/or the second aspect, the driver module may be configured to vary a duty cycle of a control signal for the semiconductor switch based on the drive signal.

In accordance with the first aspect and/or the second aspect, the heating system may comprise a controller configured to generate the drive signal.

In accordance with the first aspect and/or the second aspect, the heating system may comprise a heat exchanger configured to allow a refrigerant to be conveyed therethrough. The heater may be configured to provide heat to the heat exchanger.

It may be that the controller is configured to: determine a temperature associated with the heat exchanger; and generate the drive signal based on the determined temperature.

It may be that the controller is configured to determine the temperature associated with the heat exchanger based on a signal from a heat exchanger temperature sensor module configured to monitor a temperature associated with the heat exchanger.

In accordance with a third aspect, there is provided a heating system for a refrigeration system, the heating system comprising: a heater disposed within a space; power terminals configured to receive electrical power from a source; a heater temperature sensor module configured to change from a first state to a second state when a temperature associated with the heater reaches exceeds a heater temperature action threshold; an electrical interlock arrangement configured to prevent supply of electrical power from the power terminals to the heater when the heater temperature sensor module is in the second state; a semiconductor switch operable to modulate supply of electrical power from the power terminals to the heater; a driver module configured to control the semiconductor switch based on a drive signal; an interruption switch configured to prevent the driver module from receiving the drive signal when in a non-conducting state; and a concentration sensor module configured to: monitor a concentration of refrigerant in the space; cause the interruption switch to be in the non-conducting state when the monitored concentration of refrigerant reaches or exceeds a concentration action threshold.

A heating system in accordance with the third aspect may comprise any suitable one of, or any suitable combination of, the features described with respect to the first aspect or the second aspect.

According to a fourth aspect there is provided a refrigeration system comprising a heating system in accordance with the first aspect, the second aspect or the third aspect.

shows a vehiclecomprising a transport refrigeration system. In the example of, the transport refrigeration systemforms a part of an over-the-road refrigerated semi-trailer having a structuresupporting (or forming) at least one climate-controlled compartmentwhich is configured to be cooled and/or heated by a TRU. The climate-controlled compartmentcan take the form of multiple compartments or have multiple zones. The structureincludes a chassis. The structuresupports the TRU. The vehiclefurther comprises a tractor unitremovably couplable to the trailer.

schematically shows a diagram of an example TRUsuitable for use within the vehicleand the transport refrigeration systemof. The TRUcomprises a vapour-compression refrigeration circuitand a heating system(which may also be referred to as a heating subsystemor, more simply, a subsystem).

The vapour-compression refrigeration circuitincludes an evaporatorwhich is configured to receive heat from the climate-controlled compartmentof the transport refrigeration systemand a condenserwhich is configured to reject heat to a thermal sink(e.g., ambient air outside of the climate-controlled compartment) when the vapour-compression refrigeration circuitis operated in a cooling mode (e.g., to provide cooling to the climate-controlled compartment). For these purposes, the vapour-compression refrigeration circuitalso includes a compressorand an expansion valve. Accordingly, the vapour-compression refrigeration circuitmay be controlled to cause heat to be removed from the climate-controlled compartment. The condenserand the evaporatorare each heat exchangers,which are configured to facilitate heat transfer heat exchange between refrigerant conveyed therethrough (e.g., through a pathway provided thereby) and an external medium (i.e., the thermal sinkand the climate-controlled compartment). The vapour-compression refrigeration circuitmay also be operable in a heating mode to provide heating to the climate-controlled compartment, as will be understood by those skilled in the art.

Before operation, the vapour-compression refrigeration circuitis charged with refrigerant. During operation, refrigerant is circulated within (e.g., conveyed around) the vapour-compression refrigeration circuitin a manner which will be understood by those skilled in the art. The refrigerant may be, in particular, an A2L refrigerant such as R454A. Such refrigerants may be relatively flammable, and may thus be referred to as a flammable refrigerant or flammable refrigerants.

The subsystemcomprises a heater(e.g., a heating element) disposed within a space (e.g., the climate-controlled compartment). The evaporatoralso forms a part of the subsystem. In the example of, the heateris provided proximal to the evaporator. Accordingly, in use, the heatermay be operated to provide heating to the evaporator. However, this disclosure envisages that the heatermay be provided elsewhere within the TRU. In general terms, the heateris configured to provide electrical heating to the TRU. The electrical systemis configured to control a supply of electrical power from the DC linkto the heaterand thereby cause the heaterto generate heat for heating the TRU. The heatergenerates heat by means of resistive (e.g., Ohmic) heating when electrical power is supplied thereto. In examples in accordance with the present disclosure, the heatermay be used for defrosting the evaporator, for preventing temperature drift in the climate-controlled compartmentwhen the vapour-compression refrigeration circuitis operated in a cooling mode (e.g., for precision cooling), and/or for supplementary heating to the climate-controlled compartmentwhen the vapour-compression refrigeration circuitis operated in a heating mode.

The subsystemcomprises a pair of power terminals,(i.e., a first power terminaland a second power terminal) at which, in use, electrical power is received from a source. The sourcemay be, for example, a DC link of the TRU. The DC link may receive electrical power from, for instance, an electrical energy storage device (e.g., a battery or a fuel cell) provided to the transport refrigeration system, a generator set (e.g., an alternator) provided to the vehicle, or an external power supply (e.g., shore power) received via an external connection port when the transport refrigeration systemis stationary.

is a schematic diagram showing an example subsystemsuitable for use with the TRUdescribed above with reference to, with like reference signs denoting similar or common features.

The subsystemcomprises a local controller(e.g., a controller). The local controllermay be referred to as a remote input-output controller (RIOC). The RIOCcomprises a first port, a second port, a third port, a fourth port, and a fifth port. Each port-functions as a physical interface between a processor of the RIOCand a respective channel-. The function of the RIOCis described in further detail below.

The subsystemcomprises an isolation arrangementelectrically coupled to the power terminals,. In turn, the isolation arrangementcomprises a first contactorand a second contactor. The first contactoris electrically coupled to the first power terminaland the second contactoris electrically coupled to the second power terminal. When each contactoris closed, electrical power can flow from the power terminals,to the heater(subject to the action of the modulation arrangementdescribed below). When each contactor,is open, electrical power cannot flow from the power terminals,to the heater(regardless of the action of the modulation arrangement). Each contactor,may be referred to as a supply switch having a non-conducting state (i.e., when open) and a conducting state (i.e., when closed). It will be appreciated that other types of switches (e.g., supply switches) may be used in place of the contactors,, and that the isolation arrangementmay comprise only a single supply switch (e.g., only one of the contactors,).

The subsystemfurther comprises a modulation arrangementcomprising a semiconductor switchand a driver module. The semiconductor switchis operable to modulate supply of electrical power from the power terminals,to the heatervia the isolation arrangementby selectively completing and breaking a conduction pathway from the first power terminalto the second power terminalthrough the heater. The driver moduleis configured to control the semiconductor switchbased on a drive signal supplied thereto. More specifically, the driver module is configured to control the semiconductor switch by providing a control signal thereto, as will be understood by those skilled in the art. The semiconductor switchmay be, for example, a solid state relay (SSR).

The third channelelectrically (and thereby communicatively) couples the third portof the RIOCto the drive moduleof the modulation arrangement. The third channelis configured to convey the drive signal from the RIOCto the drive module. As a result, the third channelmay be referred to as a drive channel. The driver moduleis configured to generate the control signal for controlling the semiconductor switchbased on the drive signal received on the drive channel. Specifically, the driver modulemay generate a control signal having a duty cycle. By way of example, the driver module may generate a substantially square wave control signal being defined by the duty cycle. When the control signal is HIGH, the semiconductor switchmay be in the conducting state whereas when the control signal is LOW, the semiconductor switchmay be in the non-conducting state. Hence electrical power can only flow from the isolation arrangementto the heaterwhen the control signal is HIGH. Accordingly, the duty cycle of the control signal defines a time-averaged amount of electrical power which flows to the heaterwhen the contactors,are closed. By varying the duty cycle (e.g., by modulating the pulse width) of the control signal, the driver modulecan vary the time-averaged amount of electrical power supplied to the heater. Accordingly, the control signal may be referred to as a pulse width modulated (PWM) control signal.

The subsystemalso comprises a heater temperature sensor module. More specifically, the heater temperature sensor moduleis a bimetallic switch(which may also be referred to as a bimetallic thermostat). The bimetallic switchis not in contact with, but is proximal to, the heater. In use, heat generated by the heateris transferred to a portion of the bimetallic switchby means of radiative heat transfer. Accordingly, a temperature of the portion of the bimetallic switchis associated with a temperature of the heater. The bimetallic switchis configured to change from a first state to a second state when the temperature of the portion thereof reaches or exceeds a threshold (i.e., a heater temperature action threshold, as referred to herein). A suitable bimetallic switchmay be a KLIXON® switch. The first state of the bimetallic switchis a closed/conducting state, whereas the second state is an open/non-conducting state. Use of a bimetallic switchas part of the heater temperature sensor moduleis preferred because it provides a robust and resettable physical switching capability for the purposes described herein. Additionally, use of a bimetallic switchas part of the heater temperature sensor moduleis advantageous because it is fast-acting and does not require any burdensome conditioning or post-processing of an output signal therefrom.

Further, the subsystemcomprises an electrical interlock arrangement(or, more simply, an interlock arrangement) adapted to control the isolation arrangement. The interlock arrangementcomprises a first port, a second port, and internal circuitry which forms part of a conduction path passing from the first port, through the second port, through the heater temperature sensor module(e.g., the bimetallic switch) and back to the first portto form an interlock loop (which may be referred to as a high voltage interlock loop or a hazardous voltage interlock loop, HVIL). When the bimetallic switchis in the closed/conducting state, the interlock loop is complete. Conversely, when the bimetallic switchis in the open/non-conducting state, the interlock loop is broken. When the interlock loop is complete and an electric current flows therethrough, the interlock arrangementpermits (e.g., and thereby causes) each contactor,to be closed, whereas when the interlock loop is broken and an electric current does not flow therethrough, the interlock arrangementpermits (e.g., and thereby causes) at least one contactor,(e.g., one or both contactors,) to be open. In this way, the interlock arrangementis configured to prevent supply of electrical power from the power terminals,to the heaterwhen the heater temperature sensor moduleis in the second state. The interlock arrangementcomprises internal circuitry which is suitable for achieving these ends, as will be familiar to those skilled in the art.

The first channelextends from the first portof the RIOCto a first splice locationlocated on the interlock loop. Accordingly, the RIOCis able to monitor a status of the interlock loop by means of a signal received from the first splice location(e.g., a signal corresponding to whether a current is flowing through the interlock loop/whether the interlock loop is complete) along the first channel(and thereby indirectly monitor which state the heater temperature sensor moduleis in). The state of the heater temperature sensor modulemay then be used as part of a software which the RIOCruns in use.

The subsystemcomprises a concentration sensor module. The RIOCis configured to provide a supply of electrical power (e.g., a drive current) to the concentration sensor modulealong the fourth channel. The concentration sensor moduleis functionally coupled to an interruption switch. The interruption switchis operable to move between a closed/conducting state (e.g., a first state) and a open/non-conducting state (e.g., a second state). The concentration sensor moduleincludes a concentration transducerwhich is configured to monitor a concentration of refrigerant within the space in which the heateris disposed. Refrigerant may be present within the space due to the development of a leak from the vapour-compression refrigeration circuitinto the space. The concentration sensor moduleis more broadly configured such that when the concentration of refrigerant within the space is below a threshold (i.e., a concentration action threshold, as referred to herein), the concentration sensor modulecauses the interruption switchto be in the first state. On the other hand, the concentration sensor moduleis configured such that when the concentration of refrigerant within the space reaches or exceeds the concentration action threshold, the concentration sensor modulecauses the interruption switchto be in the second state. If a leak resulting in the presence of refrigerant within the space is relatively small, it may be that the concentration of refrigerant within the space remains less than the concentration action threshold because of diffusion of refrigerant out of the space into a surrounding environment. If so, the existence of the leak will not lead to the concentration of refrigerant within the space reaching or exceeding the concentration action threshold and thus the interruption switchwill remain in the first state.

The interruption switchis located on the drive channel. Consequently, the interruption switchis arranged within the subsystemsuch that, when in the first state, the drive signal can be supplied from the RIOCto the driver modulealong the drive channel. Conversely, when the interruption switchis in the second state, the drive channelis interrupted such that the drive signal cannot be supplied from the RIOCto the driver modulealong the drive channel.

The second channelextends from the second portof the RIOCto a second splice locationlocated on the drive channelbetween the interruption switchand the driver module. The RIOCis configured to monitor transmission of the drive signal along the drive channelby means of a signal received from the second splice locationalong the second channel(and thereby indirectly monitor which state the interruption switchis in). The state of the interruption switchmay then be used by the software which the RIOCruns in use. In particular, the interruption switchbeing in the open/non-conducting state corresponds to the concentration of refrigerant within the space reaching or exceeding the concentration action threshold. The software run by the RIOCmay make cause the RIOCto take various actions in response to a determination, based on the signal received along the second channel, that the concentration of refrigerant within the space reaches or exceeds the concentration action threshold (e.g., transmitting information relating to this determination to a central controller of the vapour-compression refrigeration circuitsuch as a main application controller (MAC), raising alerts, causing shutdown of other components and the like).

The subsystemalso comprises a heat exchanger temperature sensor moduleconfigured to monitor a temperature associated with the evaporator. The heat exchanger temperature sensor moduleis electrically and communicatively coupled to the RIOCvia the fifth channel. Accordingly, the RIOCis configured to determine a temperature associated with (e.g., of) the evaporatorbased on a signal received from the heat exchanger temperature sensor modulealong the fifth channel.

In use, the RIOCgenerates the drive signal and attempts to transmit the drive signal to the driver modulealong the drive channel. More specifically, the RIOCgenerates the drive signal based on the temperature associated with the evaporatoras discussed in greater detail below.

In, the subsystemis in a first mode. In the first mode, the bimetallic switchis in the first state thereof and the interruption switchis in the first state thereof. As a result, during operation, the isolation arrangementreceives electrical power from the power terminals,while the driver modulecontrols the semiconductor switchbased on the drive signal produced by the RIOC. Accordingly, electrical power flows from the power terminals,to the heatervia the isolation arrangementand the modulation arrangement. The amount of electrical power which flows in this way is dependent on the duty cycle of the drive signal as discussed above.

In, the subsystemis in a second mode. In the second mode, the bimetallic switchis in the first state thereof and the interruption switchis in the second state thereof. As a result, during operation, the isolation arrangementreceives electrical power from the power terminals,but the driver moduledoes not receive a drive signal from the RIOCand thus no control signal is provided to the semiconductor switch. The semiconductor switch is therefore expected to be in the non-conducting state.

In, the subsystemis in a third mode. In the third mode, the bimetallic switchis in the second state thereof and the interruption switchis in the second state thereof. As a result, the interlock arrangementcauses the isolation arrangementto prevent supply of electrical power from the power terminals,to the heaterby opening the contactors,.

The heateris, in principle, capable of acting as an ignition source with respect to any refrigerant present within the space in which the evaporatoris disposed. Generally, the heaterwill act as an ignition source in this way if the heaterapproaches the autoignition temperature of the refrigerant and the concentration of refrigerant within the space reaches or exceeds a lower flammability limit (LFL) thereof. The heatermay be especially capable of acting as an ignition source for the refrigerant within the space if a voltage supplied to the heater(e.g., by the source/DC link) is relatively high and is subject to variation in use. For example, if the heater is rated for 6 KW at 700 VDC and the voltage supplied to the heater increases by around 21% to 850 VDC, the power output of the heater will increase by around 47% to 8.84 KW. This may result in the temperature of the heaterincreasing substantially and thus approaching, reaching or exceeding the autoignition temperature of the refrigerant.

When in the first mode (see), the RIOCgenerates the drive signal based on the signal received from the heat exchanger temperature sensor moduleand supplies the drive signal to the driver modulealong the drive channel. The driver modulethen controls the semiconductor switch using the control signal which has been generated based on the drive signal.

As an example, the RIOCmay generate the drive signal based on a lower heat exchanger temperature action threshold and an upper heat exchanger temperature action threshold as well as the signal received from the heat exchanger temperature sensor module. If the signal received from the heat exchanger temperature sensor module is less than the lower heat exchanger temperature action threshold, the RIOCmay generate a drive signal corresponding to a high power demand for the heater. The control signal generated by the driver modulebased on such a drive signal may have a relatively high duty cycle. On the other hand, if the signal received from the heat exchanger temperature sensor module is greater than the upper heat exchanger temperature action threshold, the RIOCmay generate a drive signal corresponding to a low power demand or a zero power demand for the heater. The control signal generated by the driver modulebased on such a drive signal may have a relatively low duty cycle. Further, if the signal received from the heat exchanger temperature sensor module is between the lower heat exchanger temperature action threshold and the upper heat exchanger temperature action threshold inclusive, the RIOCmay generate a drive signal corresponding to an intermediate power demand for the heaterand the control signal generated by the driver module may be generated accordingly.

The signal received from the heat exchanger temperature sensor module being less than the lower heat exchanger temperature action threshold may correspond to a nominal condition of the subsystem. The signal received from the heat exchanger temperature sensor module being greater than the upper heat exchanger temperature action threshold may correspond to a shutdown fault condition in the subsystemand the RIOCmay generate a zero power demand for the heaterwith the intention of shutting down operation of the heaterfor the sake of safety considerations. The signal received from the heat exchanger temperature sensor module being between the upper heat exchanger temperature action threshold and the lower heat exchanger temperature action threshold may correspond to a warning fault condition in the subsystemand the RIOCmay generate an intermediate power demand for the heaterwith the intention of constraining operation of the heaterfor the sake of safety considerations while allowing the heaterto continue operating.

As another example, the RIOCmay generate the drive signal based on a heat exchanger temperature setpoint as well as the signal received from the heat exchanger temperature sensor module. To this end, the RIOCmay execute a proportional, integral, and/or derivative control regime based on the heat exchanger temperature setpoint.

If, however, the concentration of refrigerant within the space in which the evaporatoris disposed reaches or exceeds the concentration action threshold, the subsystemmoves into the second mode (see). In the second mode, although the RIOCmay continue to generate the drive signal based on the signal received from the heat exchanger temperature sensor module, the drive signal cannot be supplied to the driver modulealong the drive channeldue to the action of the interruption switch. Accordingly, regardless of the action of the RIOC, the driver modulewill not generate a control signal for the semiconductor switchwhen the concentration of refrigerant within the space in which the evaporatoris disposed reaches or exceeds the concentration action threshold.

Accordingly, in the second mode, it is expected that electrical power will not be supplied to the heaterbecause the semiconductor switchshould be in the non-conducting state, and thus the temperature associated with the heatermonitored by the heater temperature monitoring modulewill begin to decline (e.g., after any transient effects within the subsystemhave taken place).

The concentration action threshold is selected so as to ensure that the interruption switchmoves into the second state and thus prevents a drive signal from being received by the driver modulebefore the concentration of refrigerant within the space approaches a lower flammability limit (LFL) thereof. For example, if the LFL of the refrigerant is 18 volume percent, the concentration action threshold may be equal to or less than 16 volume percent.

Nevertheless, if the temperature associated with the heatermonitored by the heater temperature monitoring moduleinstead increases to the heater temperature action threshold when the subsystemis in the second mode, the subsystemmoves into the third mode (see). In the third mode, the bimetallic switchis in the second state and therefore the interlock loop of which it forms a part is broken. Consequently, the interlock arrangementcauses the isolation arrangementto isolate the power terminals,from the modulation arrangementand the heaterby opening the contactors,. It follows that, in the third mode, power cannot be supplied from the power terminals,to the rest of the system due to the isolation provided by the isolation arrangement.